According to Sonos, “Sonos products must be running S2 software in order to play Ultra HD audio”.

https://support.sonos.com/en-us/services/amazon-music

I’d suggest you do a lot of research on the actual, audible to you, benefits of higher definition audio before you spend a pile of money getting it working for you.

Thanks for the reply but I find that with audio it's always down to personal taste and I could probably find in research  as many people saying it's great and say its not worth it hence me trying to find a cost effective route to try it. I already have amazon uhd. Just need to find a way to play it. Maybe I need to find a cheap second hand connect s2 if the ZP90 doesn't support it via the digital out. 

If your DAC had a suitable readout it would actually show 24 bits for the signal from your ZP90. The S/PDIF has always been 24 bits wide, in order to accommodate volume adjustment of the original 16-bit input without data loss (down to around -48dB).

Bear in mind that, unless you’re planning to lock the ZP/Connect in Fixed Volume mode, any 24-bit UHD input from Amazon will suffer truncation. Lower the volume by 24dB and you’d be down to 20 bits.